Field of the Disclosure
The present disclosure relates to orthopedic joint resurfacing and/or replacement devices and systems. The present disclosure also relates to constructs, designs, materials and methods of use and manufacture of articulating devices, as well as protection of metallic junctions and fittings thereof. More specifically, the present disclosure advantageously addresses distinct aspects of orthopedic joint replacement and/or resurfacing systems and methodologies that are applicable to all joint and spinal disc locations in the body, and that in exemplary implementations effectively enhance overall efficacy and performance by combined implementation and/or utilization of (i) an integral titanium alloy composite structure having two sides—on one side an ultra-porous structured titanium alloy bone fixation surface and on the opposing side an integral solid articular surface—wherein the composite structure may be advantageously fabricated using an additive manufacturing process, (ii) an overall device design that delivers advantageous isoelasticity to bone, (iii) a thin film ternary ceramic coating applied to one or both opposed surfaces of a replacement or resurfaced device/system, and (iv) coating functionalization of one or both implant surfaces to increase hydrophilicity to (1) improve articular wear on one side, and (2) to promote osteoblast activity on the bone fixation side.
Additional features, functions and applications of the disclosed devices, systems and methods will be apparent from the description that follows.
Related Background Art
Natural joint articulation is stable and virtually wear-free due to the biological, mechanical, and tribological anatomy. However, when replacing natural articulation (e.g., due to deformity, degeneration, trauma, disease, etc.) through total joint replacement or joint resurfacing, synthetic materials are substituted in whole or in part for the anatomic living cartilage and physiologic geometries. It has been challenging for synthetic materials (e.g., metal, ceramic and polyethylene materials, etc.) to perform well under joint loading conditions within the biologic environment of the human body. In order for the joint articulation surfaces to be replaced by synthetic materials and designs, other factors must be considered, specifically those of fixation of the synthetic articulation to host bone, and the protection of any modular fittings or junctions that comprise the joint replacement of resurfacing implants.
In view of these considerations, there are at least three materials/design factors that require increased attention: i) the articulating interfaces of the joint replacement; ii) modular fittings, junctions, or couplings that make up the construction of the implant, and iii) the bone fixation surface of the implant that allows for durable stability of the implant in host bone.
Regarding the articulating interfaces of the implant, wear of the articulation surfaces can be problematic, and debris from such wear has caused bone lysis and tissue toxicity in some designs and materials. This wear can be accelerated through the introduction of third body particles that are generated at the articulating interface and elsewhere, and by surface scratches.
Regarding modular fittings and junctions, wear and fretting of modular fittings has been shown to be increasingly problematic and has resulted in galvanic, crevice and/or fretting corrosion of these implant surfaces. Patients receiving implanted joint or spinal replacement devices undergo millions of gait cycles during the course of their implant lifespan, where even minor relative, but unintended, motion could be a source for metal-metal wear, which could result in the release of wear debris particles and metal ions into the host tissues and/or into undesirable articulation between metal-on-metal components and/or metal-on-polyethylene components and associated wear. There is a danger, particularly for younger and/or active patients, of eventual wear and/or subsequent loosening of the device from host bone due to a biologic reaction to wear debris. Wear particles present in the abutting articulation region have been shown in particular to accelerate ultrahigh molecular weight polyethylene (UHMWPE) wear, carrying with it potential consequences of particulate-generated bone lysis and component failure that may result in ultimate failure of the joint replacement itself.
In addition, particulate debris generation could occur with backside wear associated with modular couplings and/or components (e.g., acetabular cups, tibial trays, etc.). For example, modular acetabular cups may include a separate polyethylene, e.g., a polyethylene liner snapped into a metal cup, which can produce micro-motion therebetween (e.g., polyethylene abrasion against a metal inner diameter wall), releasing debris particles that can induce bone lysis.
Further, there exists a known galvanic reaction between any two dissimilar metals, or metallic interfaces intended to be locked but that undergo relative motion, especially in the presence of a conductive medium, such as body fluid, that may lead to galvanic corrosion and/or release of metal particles and metal ions into host tissue. Certain metal ions are generally toxic to tissue.
Regarding the bone fixation interface, implant fixation to bone has been challenged by increased patient activity, the presentation of younger patients for arthroplasty, and by stress shielding. Stress shielding is generally caused when the implant construct is considerably stiffer than its supporting bone, bypassing the bone of necessary stress and causing its resorption, de-mineralization, and loss of strength. Bone of lesser density is more susceptible to microfracture and/or invasion by wear debris, which may accelerate the lysis and loosening cycle.
Also regarding implant fixation and biocompatibility of the bone fixation interface, release of metal ions can have an untoward effect. Oxidation of both the debris and freshly exposed metal surfaces associated with joint repair/replacement reduces oxygen and pH levels of the trapped body fluids. This phenomenon may accelerate breakdown of the metal surface passivation layer by creating conditions that increase the solubility of the metal oxide film associated with a metal implant. Additionally, oxidized debris is typically harder than the surfaces from which it came and acts as an abrasive third body agent that can increase the rate of fretting. Indeed, the processes may feed off each other.
An additional goal in orthopedic joint replacement or resurfacing procedures is to mitigate third body particulate debris that can develop due to the breakdown of bone cement. Therefore, joint replacement using a cementless fixation device has become a common and desired procedure for addressing osteoarthritis (arthrosis) in patients afflicted with the condition. The cementless fixation procedure may involve the use of a stiff solid metal device with surfaces intended for biologic fixation of the device to bone. Many metal devices are generally stiffer than the bone to which they are affixed by the nature of their design. This mismatch in stiffness can result in the biologic loss of bone density surrounding and supporting the solid metal device (e.g., by stress shielding), which can result in the eventual loosening of the device from the host bone.
As is apparent, there is a need in all forms of orthopedic (i) articulation, (ii) modular junction couplings and interfaces, and (iii) implant fixation, to eliminate and/or reduce generation of wear and wear debris, to increase surface wettability and lubricity for wear reduction, reduce the potential for fretting and corrosion, to reduce/eliminate the occurrence of stress shielding, and to increase overall durability of the orthopedic device fixation through maintained host bone support, as well as to protect those surfaces from metal particle and ion release.
In addition, in view of the challenges outlined above, there is a need for orthopedic joint replacement and/or joint resurfacing devices, systems and methods that are fabricated to protect modular interfaces from direct metal-metal contact, particulate debris, fretting, wear, galvanic corrosion, and crevice corrosion, in whole or in part. There is also a need for orthopedic joint replacement and/or joint resurfacing devices, systems and methods that include articulation surfaces and/or substrates that effectively load supporting bone from a physiologic standpoint, thereby avoiding loss of bone density through stress shielding. Indeed, there is a need for joint replacement and/or joint resurfacing devices, systems and methods that deliver isoelastic functionality that closely replicates the stiffness of the host bone to maintain healthy bone density and fixation of the device within the patient and that is biocompatible, meaning that host bone has an affinity to the fixation surface of the implant.
These and other needs are satisfied by the orthopedic joint replacement and joint resurfacing devices, systems and methods disclosed herein, including specifically the advantageous coating materials and coating systems disclosed herein for use in orthopedic joint replacement and joint resurfacing modalities.